1. Field of the Invention
The present invention relates to an air-cycle air conditioning system for use, particularly, in an automotive vehicle.
2. Description of the Related Art
A vapor-cycle air conditioning system has been widely used in motor vehicles. This system utilizes a coolant such as freon so as to obtain a cooling air. Various attempts have hitherto been made to improve such a system.
In connection with environmental disruption, it has recently been found that freon may damage an ozone layer in the Earth and result in the rise of temperature. Thus, there is an increasing need for an air conditioning system with an alternative coolant.
Attention is now paid to an air-cycle air conditioning system as an alternative air conditioner. This system has been used in an aircraft and uses a bleed air pressure in an engine or an auxiliary power unit (APU). A cooling turbine expands and cool the air so as to provide a cooling air. The aircraft is not subject to a substantial change in the engine load during operation. Also, there is a little change in the bleed air pressure. This enables a constant supply of cooling air. When such an air-cycle air conditioning system is used in an automotive vehicle, an additional drive source is required to drive a cooling turbine. Such a cooling turbine can be driven by energy of exhaust gases from a vehicle engine. However, engine load is likely to vary during operation of the vehicle engine. This results in the change of energy of the exhaust gases. A constant supply of cooling air is not guaranteed.